1. Field of the Invention
This invention relates to an injection mold, and more particularly to an improvement of an injection mold suitable for in-mold decorating in which a transfer film is positioned in the cavity of the mold before injection of injection material so that the design on the transfer film is transferred to the surface of the molded article.
2. Description of the Prior Art
There has been known an art of providing a design on an injection-molded article by injection-molding the article with a transfer film bearing thereon the design being inserted into the cavity of the injection mold. This art is generally referred to as "in-mold decorating". That is, the transfer film generally comprises a base film, and a releasant layer, an ink layer representing the design and an adhesive layer laminated on the base film in this order, and when molding material is injected into the cavity with the transfer film being in the cavity, the transfer film is bonded to the surface of the molded article after the molding material is solidified. When the base film is peeled off after the article is removed from the cavity, the ink layer is transferred to the surface of the article by virtue of the releasant layer.
In-mold decorating using a transfer film will be now described in more detail with respect to in-mold decorating of a cassette half by way of example. The cassette body 20 as shown in FIG. 7 is injection-molded by use of a mold comprising a stationary mold half 1 and a movable mold half 2 as shown in FIG. 4. The halves 1 and 2 are respectively provided with recesses 3 and 4 for forming, when the mold is closed, a cavity having a shape conforming to the shape of the cassette half 20. Since the cassette half 20 has openings such as hub holes 21, a window 22, reference holes 23, and capstan holes 24 as shown in FIG. 7, like numbers of coring pins are provided in the stationary mold half 1 to project into the cavity and abut against the bottom of the recess 4 of the movable mold half 2 with a transfer film 10 intervening therebetween when the mold is closed. In FIGS. 4 and 5, only coring pins 5 and 6 for forming one of the hub holes 21 and one of the capstan holes 24 are shown. Further, the stationary mold half 1 is provided with a sprue 1a through which injection material is injected into the cavity.
With the mold is opened, i.e., the movable mold half 2 is positioned away from the stationary mold half 1, the transfer film 10 is positioned in place between the mold halves 1 and 2 as shown in FIG. 4. Thereafter, the mold is closed by bringing the movable half 2 into close contact with the stationary half 1, and injection material 7 is injected into the cavity through the sprue 1a to fill it as shown in FIG. 5. The transfer film 10 comprises a releasant layer 12, an ink layer 13 and an adhesive layer 14 laminated on a base film 11 in this order as shown in FIG. 6, and the transfer film 10 is positioned so that the injection material 7 fills the cavity on the side of the adhesive layer 14. Accordingly, the transfer film 10 is bonded to the molded cassette body by the adhesive layer 14. By peeling the base film 11 after the injection material 7 is solidified and the molded cassette body is removed from the mold, the ink layer 13 is transferred to the surface of the molded cassette body.
However, there has been a problem in such in-mold decorating that the front end faces 5a and 6a of the coring pins 5 and 6 for forming the hub hole 21 and the capstan hole 24, for instance, directly abut against the adhesive layer 14, and the ink layer 13 is transferred to the front end faces 5a and 6a when the mold is opened. As the molding cycles are repeated, the stacked ink layers on the front end faces 5a and 6a can cause finning around the hub hole 21 and the capstan hole 24. Further, the ink layer can subsequently peel from the front end faces 5a and 6a to contaminate the molded cassette body.